Conducting polymer coated neural recording electrodes

Abstract

Neural recording electrodes suffer from poor signal to noise ratio, charge density, biostability and biocompatibility. This paper investigates the ability of conducting polymer coated electrodes to record acute neural response in a systematic manner, allowing in depth comparison of electrochemical and electrophysiological response. Approach. Polypyrrole (Ppy) and poly-3,4-ethylenedioxythiophene (PEDOT) doped with sulphate (SO4) or para-toluene sulfonate (pTS) were used to coat iridium neural recording electrodes. Detailed electrochemical and electrophysiological investigations were undertaken to compare the effect of these materials on acute in vivo recording. Main results. A range of charge density and impedance responses were seen with each respectively doped conducting polymer. All coatings produced greater charge density than uncoated electrodes, while PEDOT-pTS, PEDOT-SO 4 and Ppy-SO4 possessed lower impedance values at 1 kHz than uncoated electrodes. Charge density increased with PEDOT-pTS thickness and impedance at 1 kHz was reduced with deposition times up to 45 s. Stable electrochemical response after acute implantation inferred biostability of PEDOT-pTS coated electrodes while other electrode materials had variable impedance and/or charge density after implantation indicative of a protein fouling layer forming on the electrode surface. Recording of neural response to white noise bursts after implantation of conducting polymer-coated electrodes into a rat model inferior colliculus showed a general decrease in background noise and increase in signal to noise ratio and spike count with reduced impedance at 1 kHz, regardless of the specific electrode coating, compared to uncoated electrodes. A 45 s PEDOT-pTS deposition time yielded the highest signal to noise ratio and spike count. Significance. A method for comparing recording electrode materials has been demonstrated with doped conducting polymers. PEDOT-pTS showed remarkable low fouling during acute implantation, inferring good biostability. Electrode impedance at 1 kHz was correlated with background noise and inversely correlated with signal to noise ratio and spike count, regardless of coating. These results collectively confirm a potential for improvement of neural electrode systems by coating with conducting polymers. 2013 IOP Publishing Ltd.

Optical and Electrochemical Methods for Determining the Effective Area and Charge Density of Conducting Polymer Modified Electrodes for Neural Stimulation

“…Many of the uncoated electrodes showed little or no oxidative charge over the potential window tested, and the ratio of oxidative to reductive charge on most coated electrodes was well below 1, in contrast to our previous results 20 . Therefore, the reductive charge was used for all subsequent data and for calculating the charge density.…”

“…This process is most likely associated with the reduction of oxygen in the non-degassed solution. Voltammetry of PEDOT-pTs was consistent with previous results 20 , displaying a relatively featureless response with large capacitance (figure S4b). PEDOT-Page 8 of 24 PSS possessed a broad reduction process around -0.6 V, shifting towards -0.43 V on thicker films and a sharper oxidation peak at -0.37 V (figure S4c) 18,19 .…”

“…para-toluene sulfonate (pTs) dopant was also tested, as previous neural recording data has shown it to have a high charge density and good acute recording performance 20 . Dodecylbenzenesulfonate (DBSA) dopant was also used, as it has a similar structure to pTs and had good cultured cell viability when used to dope polypyrrole [21][22][23] .…”

“…Dodecylbenzenesulfonate (DBSA) dopant was also used, as it has a similar structure to pTs and had good cultured cell viability when used to dope polypyrrole [21][22][23] . PEDOT-PSS and PEDOT-DBSA were deposited for 4 different times (15,30,45 or 60 s), PEDOTpTs was deposited for 45s as recommended in our previous article 20 . 2 probes were coated with PEDOT-PSS and 2 with PEDOT-DBSA, 4 electrode sites coated at each deposition time in a staggered array as previously described 20 , leaving 12 uncoated platinum electrodes and 4 PEDOTpTS coated electrodes as controls.…”

Taking Electrons out of Bioelectronics: From Bioprotonic Transistors to Ion Channels

“…Silicon nanowire and carbon nanotube transistors integrated with enzymes, antibodies, and lipid bilayers use ions to gate electronic currents and record biological reactions in the intracellular and extracellular space 2, 3, 9, 10, 11, 12, 13, 14, 15, 16. Organic polymers with mixed electronic and ionic conductivity integrated in electrodes and electrochemical transistors transduce ionic to electronic currents and amplify small biological signals3, 17, 18, 19, 20, 21, 22 In addition, organic iontronics locally deliver ions and neurotransmitters in the extracellular space to affect cell and tissue function 23, 24, 25, 26. Batteries with biocompatible materials are used for giving energy to these systems 27.…”